Exchange interactions between orbitally degenerate ions. The case of two 2Eg ions

Abstract

The problem of the exchange interaction between two ²E_g ions forming a pair of D_4h symmetry is studied. As a first step, a general method is proposed to determine the symmetries of the terms arising from the interaction, and the energies of these terms are calculated from the true electrostatic Hamiltonian. As a second step, a phenomenological model, invariant with respect to a unitary transformation between the atomic orbital basis functions and leading to the same terms as the true electrostatic perturbation, is described.